This invention relates to a collapsible bow saw comprising a frame and a long saw blade which, when the saw is stretched in use is tight between opposite end portions of the frame. The frame is composed of three individual hollow elements, namely a main element extending in spaced relation to the saw blade and two end elements which, when the saw is in use, extend between the ends of the main element and the ends of the blade and which are connected to the main element while forming a rigid frame as long as a tensile stress is maintained in the blade. The main element and the end elements have different cross sectional dimensions so as to allow the elements to be telescoped into each other. after separation of the end elements from the saw blade and to allow the blade to be telescoped into a sheltered position in the cavities of said elements.
Collapsible bow saws are previously known, as in U.S. Pat. No. 2,930,420 and German Offenlegungsschrift No. 1,926,446. These saws do, however, suffer from a number of drawbacks, e.g. poor rigidity of the frame when in a mounted condition and high manufacturing costs due to the fact that the frame is composed of a great number of components which call for a plurality of working moments.
In the saw disclosed in the above-mentioned U.S. Pat. No. 2,930,420, neither the main element nor the end elements have box profiles with closed cross sections. Instead they have U-shaped profiles with open slots through which the saw blade passes when the saw is collapsed and mounted, respectively. These slots drastically reduce the inherent rigidity of the three frame elements and make them apt to become distorted or deformed as soon as the saw blade is subjected to even moderate tensile stresses. Furthermore the end elements are intended to be introduced into the main element and not the other way around, so that the portion gripped by the hand of the user will be more slender than the main element and thereby less comfortable to manipulate. To this should be added the fact that an individual connection between the main element and one of the end elements calls for special stop pins and special guiding grooves having a complicated shape. This makes the construction unsuitable for convenient mass production.
In German Offenlegungsschrift No. 1,926,446 it is true that the main element itself has a box profile with a closed cross section, but the two end elements consist of thin, slender, flat bars which on one hand are not capable of giving the desired rigidity to the frame in its entirety and on the other hand are not suited for gripping by the hand of the user. For the last-mentioned reason it is necessary to arrange a special handle, which considerably increases the price of the saw in its entirety. Moreover the construction is unsuitable for convenient mass production since the connection between the main element and a single end element requires a plurality of operations and a plurality of components in the shape of separate gable plates, stop screws, springs, balls, et cetera. Put together these factors mean that the total manufacturing cost becomes extremely high and that the saw is consequently poorly competitive in commerce.